Determines when the squeezer will switch children.
If set to [adw.types.FoldThresholdPolicy.Minimum], it will only switch when the visible child cannot fit anymore. With [adw.types.FoldThresholdPolicy.Natural], it will switch as soon as the visible child doesn't get their natural size.
This can be useful if you have a long ellipsizing label and want to let it ellipsize instead of immediately switching.